As for a vehicle body reinforcing device that can be attached to an existing vehicle, there is known heretofore the vehicle body reinforcing device that is supported on the vehicle body by brackets disposed at both axial ends of the device. For example, in Patent document 1 as listed below, “in order to provide a reinforcement device for the vehicle body frame that makes it possible to easily improve ride comfort by attachment or removal of the reinforcement member according to the preference of the driver” as an object (described in Paragraph (0011) of Patent document 1), with respect to “the vehicle body reinforcement device formed in elongated shape and with a force generating means for generating a hydraulic damping force against its longitudinal deformation interposed in its middle”, the vehicle body reinforcing device defined by various requirements has been proposed (described in Paragraph (0012) of the same).